1. Field of Invention
The present invention relates to a sealed type compressor having sliding members to compress HFC refrigerants and refrigerating cycle using the sealed type compressor.
2. Description of Related Art
Refrigerating cycles are broadly used in refrigerating equipment, such as refrigerators and refrigerated showcases, and in air conditioners which cool and/or heat the insides of rooms. Sealed type compressors which compress and circulate the refrigerant are used in these refrigerating cycles.
The sealed type compressor has a sealed case, a motor and compression machinery which is driven by this motor. Both the motor and the compression machinery are inside of the sealed case. In a refrigeration cycle, a refrigerant is compressed by the compressor, and discharged at high temperature and high pressure to circulate through the refrigeration cycle.
It is known to use, in refrigerating cycles including those which include sealed type compressors, chlorofluorocarbon refrigerant CFC12 (hereafter, "R12 refrigerant") or hydrochlorofluorocarbon refrigerant HCFC22 (hereafter, "R22 refrigerant") as a refrigerant. The compressors include sliding members to compress the refrigerant. Such compressors require that oil be supplied to lubricate these sliding members. Naphthene group and paraffin group mineral oils with superior compatibility with R12 and R22 refrigerants have been used as the oil for lubricating such compressors.
When using R12 as the refrigerant, chlorine (Cl) atoms in the R12 react with iron (Fe) atoms of metal base material to form an iron chloride film on the surface of iron based materials. The iron chloride film has self-lubricating properties and high wear resistance. The iron chloride film prevents iron based material from contacting another sliding member which causes wear.
An additional benefit of using R12 is that R12 and the conventional refrigerating machine oil are non-polar. Thus, both have a low absorbency. Therefore, the iron chloride film formed on the iron base material exists as a stable lubricating film without hydrolysis taking place.
However, R12 refrigerant is chemically extremely stable in the atmosphere. Therefore, even small amounts of R12 refrigerant exhausted into the atmosphere reach the ozone layer, and damage it. Accordingly, R12 has been designated to be a specific Freon that damages the ozone layer and has been subjected to severe limitations in its use. On the other hand, R22 refrigerant easily decomposes in the atmosphere and therefore has been designated as a specific Freon that causes less (although it still causes some) damage the ozone layer. Therefore, it has been decided, as a matter of international policy, to curtail the use of R22 refrigerant as well.
In view of the ozone damage problem, recently, HFC (hydrofluorocarbon) refrigerants which do not cause ozone damage, have been developed as substitute Freons to replace the specific Freons designated to be harmful. However, HFCs do not have chlorine atoms (sometimes they are referred to as non-chlorine refrigerants). Thus, there is no natural self lubricating that occurs by the combination of iron and chlorine.
Furthermore, when a sealed-type compressor operates with HFC refrigerant and uses a naphthene group or paraffin group mineral oil as its machine oil, the naphthene group or paraffin group mineral oil does not dissolve in HFC refrigerant. There is poor compatibility between these oils and HFC refrigerants. Return of oil discharged from the sealed-type compressor into the refrigerating cycle is poor and lubrication and cooling of sliding members of the compressor suffers. In the worst case, the poor lubrication causes a fusing of sliding members of the compressor. For this reason, it is necessary to develop a refrigerating machine oil having better compatibility with HFC refrigerants. In fact, the development of various refrigerating machine oils is progressing. Among these, PAG (polyalkyleneglycol) oil, which has been widely adopted for car air conditioners, has good compatibility with HFC refrigerant.
However, PAG oil has low volume resistivity, and low electric insulation resistance. Therefore, it cannot be used in sealed-type compressors in which an electric motor is immersed in machine oil.
Other oils recently attracting attention for possible use in sealed-type compressors are ester oils which are synthesized from fatty acids and alcohols. Ester oils have excellent compatibility with HFC refrigerants, and they are superior to mineral oil in their resistance to heat. They also have thermal stability (heat resistance) and a good electric insulation resistance. However, their resistance to hydrolysis and their wear resistance vary greatly depending on the base oil chemical structure. Furthermore, its lubrication ability is poorer than that of a conventional combination of CFC refrigerant and HCFC refrigerants with mineral oil.
For example, when ester oil is used to lubricate a sealed-type compressor operating with HFC refrigerant, the wear resistance properties of cast iron, carbon steel, alloy steel, sintered alloy or stainless steel, etc. used for the sliding members of the compressor is lower. Thus, the compressor cannot be operated stably over a long period of time.